Semi-Physical Behavioral Modeling of Radio Frequency Power Amplifiers for the Optimization of the Linearity-Efficiency Tradeoff

The demand for higher data rates and the increased number of mobile subscribers within the limited frequency spectrum has given rise to the use of complex modulation schemes in mobile communications. As a result communication signals of the latest mobile communication standards, such as Wideband Code Division Multiple Access (WCDMA) and Long Term Evolution (LTE), exhibit high Peak to Average Power Ratios (PAPRs). The amplitudes of such signals vary over a wide range. As a consequence, the Power Amplifier (PA), representing the last amplification stage of the transmitter, is backed off from saturation in order to satisfy the strict linearity requirements demanded by the mobile communication standards. This decreases the efficiency considerably because the PA is most efficient when it is operated at saturation. Supply voltage modulated PAs achieve high efficiency even though they are excited by communication signals featuring high PAPRs. Due to their promising energy efficiency, supply voltage modulated PAs have become a hot research topic. Systems that operate the PA as such are highly complex. In order to cope with the increased complexity and to enable early assessments of the quality of the system design, rapid prototyping simulations must be accomplished.

This work lays the foundation for studying and optimizing the linearity-efficiency tradeoff in simulations. As state of the art behavioral models are inappropriate for such studies, a novel, semi-physical behavioral modeling framework addressing the Amplitude-Modulation-to-Amplitude-Modulation (AM-AM), Amplitude-Modulation-to-Phase-Modulation (AM-PM), and Amplitude-Modulation-to-DC-Current-Modulation (AM-IM) characteristics of PAs is introduced. The accuracy of the behavioral models is validated using actual industrial applications of Gallium Arsenide (GaAs)-based and Complementary Metal Oxide Semiconductor (CMOS)-based PAs. The excellent results obtained for single PAs and for an idealized Envelope Tracking (ET) transmitter show that it is possible to optimize the PA in terms of linearity and efficiency early in the design phase. This highlights the potential for reducing the design time and avoiding the costs of redesigning hardware.